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Searching for high-efficiency photocatalysts for overall water splitting is a promising strategy to solve the energy crisis and environmental problems. Among many kinds of photocatalysts, direct Z-scheme systems have attracted much attention. Here, we propose two-dimensional arsenene/ZrS2(HfS2) heterostructures as potential direct Z-scheme photocatalysts based on density functional theory simulations. Our calculations demonstrate that arsenene/ZrS2(HfS2) heterostructures have type-II band alignments with small band gaps, facilitating spatial separation of photo-generated carriers and enhancing sunlight absorption ability. Meanwhile, interlayer charge transfer induces a built-in electric field, resulting in the band edge positions bending at the interface region. Combined with the closed band edge positions and small interlayer band gaps, the direct Z-scheme charge transfer pathway is confirmed for them. Additionally, both heterostructures show energic, dynamical, and thermal stability based on the calculated results. What is more, under solar irradiation, the hydrogen evolution reaction and oxygen evolution reaction can be triggered spontaneously on different monolayers with the potential supplied by photo-generated electrons and holes based on the calculated free energy difference (ΔG). Therefore, arsenene/ZrS2(HfS2) heterostructures may have promising potential as bifunctional photocatalysts for overall water splitting. This work provides valuable guidance for designing the direct Z-scheme photocatalysts.

We have investigated the Josephson coupling between two s-wave superconductors separated by the ferromagnetic trilayers with noncollinear magnetization. We find that the long-range triplet critical current will oscillate with the strength of the exchange field and the thickness of the interface layer, when the interface magnetizations are orthogonal to the central magnetization. This feature is induced by the spatial oscillations of the spin-triplet state |↑↓ +|↓↑ in the interface layer. Moreover, the critical current can exhibit a characteristic nonmonotonic behavior, when the misalignment angle between interface magnetization and central ferromagnet increases from 0 to π/2. This peculiar behavior will take place under the condition that the original state of the junction with the parallel magnetizations is the π state.

We theoretically study the valley- and spin-resolved scattering through magnetic barrier in a one layer thick silicene, using the mode-matching method for the Dirac equation. We show that the spin-valley filtering effect can be achieved and can also be tuned completely through both a top and bottom gate. Moreover, when reversing the sign of the staggered potential, we find the direction of the valley polarization is switched while the direction of spin polarization is unchanged. These results can provide some meaningful information to design valley valve residing on silicene.

Searching for two-dimensional semiconductor materials that are suitable for visible-light photocatalytic water splitting provides a sustainable solution to deal with the future energy crisis and environmental problems. Herein, based on first-principles calculations, single-layer ZnMN2 (M = Si, Ge, Sn) zinc nitrides are proposed as efficient photocatalysts for water splitting. Stability analyses show that the single-layer ZnMN2 zinc nitrides exhibit energetic and dynamical stability. The electronic properties reveal that all of the single-layer ZnMN2 zinc nitrides are semiconductors. Interestingly, single-layer ZnSnN2 is a direct band gap semiconductor with a desirable band gap (1.74 eV), and the optical adsorption spectrum confirms its optical absorption in the visible light region. The hydrogen evolution reaction (HER) calculations show that the catalytic activity for single-layer ZnMN2 (M = Ge, Sn) is better than that of single-layer ZnSiN2. Furthermore, the band gaps and band edge positions for the single-layer ZnMN2 zinc nitrides can be effectively tuned by biaxial strain. Especially, single-layer ZnGeN2 can be effectively tuned to match better with the redox potentials of water and enhance the light absorption in the visible light region at a tensile strain of 5%, which is confirmed by the corresponding optical absorption spectrum. Our results provide guidance for experimental synthesis efforts and future searches for single-layer materials suitable for photocatalytic water splitting.